The present invention relates to a process for stabilizing a solution containing a peroxidic compound used for the bleaching of products such as textiles and paper pulps.
Bleaching of different materials such as textiles and paper pulps can be carried out using various peroxidic compounds. Among the latter, hydrogen peroxide and sodium peroxide are often employed, hydrogen peroxide being used preferentially.
Solutions containing only hydrogen peroxide are relatively ineffective in bleaching, and therefore, it is essential to activate them by the addition of alkalis in order to improve the bleaching power. Sodium hydroxide is frequently used to this end. However, if the alkaline agent is added alone, it induces much too rapid and much too great a decomposition of the hydrogen peroxide, so that a not insignificant part of the latter is lost for bleaching.
Consequently, this has led to the simultaneous introduction of stabilizers into the bleaching medium in such a way as to control the decomposition of the hydrogen peroxide induced by the basic compound. The relative concentration of stabilizer/basic compound is chosen so as to ensure the best bleaching power.
In the past, several stabilizers have been proposed. Among these, one of the most commonly used is sodium silicate. However, sodium silicate suffers from the disadvantage of giving a rough feel to the bleached materials, which proves particularly objectionable in the field of tissue papers and of textiles. In addition, for textiles, it gives rise to encrustation phenomena which are also very objectionable.
Other organic-type compounds have also been proposed as stabilizers for peroxidic solutions. Among these, the magnesium salts or complexes of the polycarboxylates and polyhydroxycarboxylates described in German Published Patent Application No. 2,035,047, filed on July 15th, 1970 by DEGUSSA, are to be mentioned particularly. However, these polymers allow neither as good a stabilization of the hydrogen peroxide, nor as good a degree of bleaching to be obtained as that obtained with sodium silicate.
Moreover, during bleaching of products such as textiles and paper pulps by solutions containing peroxidized compounds, one observes a degradation of the cellulosic chains and a reduction in their degree of polymerization, which leads to a reduction in the mechanical strength (to tearing, tension, bursting (or rupture), etc.) of the finished products. The hydrogen peroxide stabilizers cited above do not assure an effective protection of the cellulosic chains against this depolymerization.